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JEE Main 2021
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

The Boolean expression (pq)q(pq)\left( {p \wedge \sim q} \right) \vee q \vee \left( { \sim p \wedge q} \right) is equivalent to :

Options

Solution

Key Concepts and Formulas

  • Distributive Law: p(qr)(pq)(pr)p \vee (q \wedge r) \equiv (p \vee q) \wedge (p \vee r) and p(qr)(pq)(pr)p \wedge (q \vee r) \equiv (p \wedge q) \vee (p \wedge r)
  • Identity Laws: pFalsepp \vee \text{False} \equiv p and pTruepp \wedge \text{True} \equiv p
  • Complement Laws: ppTruep \vee \sim p \equiv \text{True} and ppFalsep \wedge \sim p \equiv \text{False}
  • Absorption Law: p(pq)pp \vee (p \wedge q) \equiv p and p(pq)pp \wedge (p \vee q) \equiv p
  • De Morgan's Laws: (pq)pq\sim (p \vee q) \equiv \sim p \wedge \sim q and (pq)pq\sim (p \wedge q) \equiv \sim p \vee \sim q

Step-by-Step Solution

Step 1: Rewrite the given expression.

We are given the Boolean expression (pq)q(pq)(p \wedge \sim q) \vee q \vee (\sim p \wedge q). Our goal is to simplify this expression using Boolean algebra laws.

Step 2: Apply the distributive law.

We can rewrite the expression by grouping the last two terms: (pq)(q(pq))(p \wedge \sim q) \vee (q \vee (\sim p \wedge q)).

Step 3: Apply the absorption law to the second group.

Notice that q(pq)q \vee (\sim p \wedge q) can be simplified using the absorption law. Specifically, q(pq)qq \vee (\sim p \wedge q) \equiv q. This is because pq\sim p \wedge q implies qq, so adding qq to it doesn't change the value. Thus, we have (pq)q(p \wedge \sim q) \vee q.

Step 4: Rearrange and apply the distributive law.

Rewrite the expression as q(pq)q \vee (p \wedge \sim q). We can rewrite this as (qp)(qq)(q \vee p) \wedge (q \vee \sim q).

Step 5: Apply the complement law.

Since qqTrueq \vee \sim q \equiv \text{True}, the expression becomes (qp)True(q \vee p) \wedge \text{True}.

Step 6: Apply the identity law.

Using the identity law, (qp)Trueqp(q \vee p) \wedge \text{True} \equiv q \vee p. Therefore, the expression simplifies to pqp \vee q.

Common Mistakes & Tips

  • Carefully apply the distributive law. Make sure you are distributing correctly over \vee and \wedge.
  • Remember the absorption law: p(pq)=pp \vee (p \wedge q) = p and p(pq)=pp \wedge (p \vee q) = p. Recognizing this can significantly simplify expressions.
  • When in doubt, construct a truth table to verify your simplifications.

Summary

We started with the Boolean expression (pq)q(pq)(p \wedge \sim q) \vee q \vee (\sim p \wedge q) and simplified it using Boolean algebra laws. We applied the absorption law, distributive law, complement law, and identity law to arrive at the simplified expression pqp \vee q.

Final Answer

The final answer is \boxed{p \vee q}, which corresponds to option (C).

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